1. Field of the Invention
The present invention relates to a method of mutually bonding substrates of which bonding surfaces contain silicon dioxide as the primary component, a detector cell produced according to this bonding method and an optical measuring apparatus, such as a capillary electrophoresis apparatus or the like, having this detector cell.
2. Description of the Related Art
To bond glass substrates to each other, there has conventionally been widely used a fusion-bonding method by which the glass substrates are heated to a temperature of the glass annealing point or more such that the glass substrates are bonded as fused. For example, substrates of borosilicate glass (Pyrex 7740 or the like) are fusion-bonded when heated to a temperature of about 560.degree. C. or more, and substrates of quartz are fusion-bonded when heated to a temperature of about 1200.degree. C. or more.
There is also disclosed an optical measuring apparatus, such as a capillary electrophoresis apparatus or the like, arranged such that a sample flowing in the passage is analyzed for components by irradiating light such as ultraviolet rays or the like onto the sample and measuring the amount of light absorbed by the sample or the amount of fluorescence emitted from the sample (for example, D. Harrison et al. Analytica Chimica Acta 283 (1993) 361-366). In such an apparatus, a groove is formed in each of a pair of glass substrates and the glass substrates are bonded to each other by the fusion-bonding method above-mentioned, thus forming a passage in which a sample is to flow.
To fusion-bond substrates of quartz, it is required to raise the temperature thereof to a level as high as 1200.degree. C., as mentioned earlier. Disadvantageously, this not only requires a special temperature raising device, but also makes it difficult to hold the quartz substrates of which temperature is being raised to such a level.
To reflect light in a multiple manner to increase the light passage length in an optical measuring apparatus in which grooves formed in the glass substrates serve as the sample passage, metallic layers are formed on the grooves in the glass substrates. Since the glass substrates are bonded to each other at an ultra-high temperature, the metallic layers are changed in quality, thus assuring no sufficient reflection efficiency. In particular, when light in the ultraviolet zone is to be used, the glass substrates to be used are limited to quartz substrates in view of the characteristics of transmittance. Further, it is preferred to use, as each metallic layer, an aluminium layer in view of reflection efficiency. However, quartz is high in melting point while aluminium has a very low degree of heat tolerance. In fusion-bonding, aluminium is therefore changed in quality. Accordingly, it is substantially difficult to use an aluminium layer as the metallic layer.
In fusion-bonding, the substrates are bonded to each other in a point-contact manner. Thus, the application of a load to the substrates is uneven. This makes it difficult to evenly bond the glass substrates in their entirety. Further, the fusion-bonding processing is executed on the glass substrates as conveyed in a thermal processing furnace. This makes it difficult to bond, to each other, the glass substrates as accurately positioned with respect to each other.
In view of the foregoing, the desired passage cannot be formed. Accordingly, the optical measuring apparatus of prior art cannot assure not only a uniform migration of a sample, but also a multiple-reflection of light with a high reflectance. Thus, a satisfactory detection precision cannot be obtained.